java中equals和==的区别(String) |
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java中equals和==的区别(String)
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话不多说,先给出String中equals方法的源码 /** * Compares this string to the specified object. The result is {@code * true} if and only if the argument is not {@code null} and is a {@code * String} object that represents the same sequence of characters as this * object. * * @param anObject * The object to compare this {@code String} against * * @return {@code true} if the given object represents a {@code String} * equivalent to this string, {@code false} otherwise * * @see #compareTo(String) * @see #equalsIgnoreCase(String) */ public boolean equals(Object anObject) { if (this == anObject) { return true; } if (anObject instanceof String) { String anotherString = (String)anObject; int n = value.length; if (n == anotherString.value.length) { char v1[] = value; char v2[] = anotherString.value; int i = 0; while (n-- != 0) { if (v1[i] != v2[i]) return false; i++; } return true; } } return false; }分析 1.代码中可以看出,方法中第一步就判断是的==,如果满足就直接返回true,否则继续往下走 if (this == anObject) { return true; }2.再看第二个if语句,先判断传过来的对象类型是否为String,然后再比较长度,最后比较的是value 从这我们就可以想到,equals方法比较的是String变量的内容是否相同 if (anObject instanceof String) { String anotherString = (String)anObject; int n = value.length; if (n == anotherString.value.length) { char v1[] = value; char v2[] = anotherString.value; int i = 0; while (n-- != 0) { if (v1[i] != v2[i]) return false; i++; } return true; } }所以,equals方法比较的是字符串内容,==判断的是是否是同一个对象,满足==必然满足equals,所以equals先判断== 给出我的练习代码 /** * equals方法测试 */ public static void equalsTest(){ System.out.println("*****equals方法和==测试*****"); //两个字符串的内容相同，不用new关键字新建对象 String firstString = "yangqi"; String firstContentCopy = "yangqi"; //两个字符串的内容相同，分别用new关键字新建对象 String secondString = new String("zhoufei"); String secondContentCopy = new String("zhoufei"); //equals方法结果 System.out.println("firstString("+firstString+") equals firstContentCopy("+firstContentCopy+")?"); System.out.println(firstString.equals(firstContentCopy));//结果为true System.out.println("secondString("+secondString+") equals secondContentCopy("+secondContentCopy+")?"); System.out.println(secondString.equals(secondContentCopy));//结果为true //==比较结果 System.out.println("firstString("+firstString.hashCode()+")==firstContentCopy("+firstContentCopy.hashCode()+")?"); System.out.println(firstString==firstContentCopy);//结果为true System.out.println("secondString("+secondString.hashCode()+")==secondContentCopy("+secondContentCopy.hashCode()+")?"); System.out.println(secondString==secondContentCopy);//结果为false }运行结果 其中,用new关键字和不用new关键字的区别,在以后的博文中探讨. |
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